Conventionally, as a method for collecting and removing particulate matters contained in a dust-containing fluid such as exhaust gas emitted from a diesel engine or the like, there is known the use of a honeycomb structure in which a wall of through channel has a filtering function, one end is clogged for predetermined through channels, and the other end is clogged for the remaining through channels.
In the case where such a honeycomb structure is used as a filter for collecting particulate matters in exhaust gas, it is necessary to perform regenerating treatment in which accumulating carbon particulates are burned and removed. At this time, a local increase in temperature is unavoidable, so that a high thermal stress is liable to occur, which poses a problem in that a crack is liable to develop.
As measures for reducing the thermal stress occurring in such a structural part, a method in which the structural part is divided into small segments is known. The use of a honeycomb structure for collecting particulates in exhaust gas has already been proposed in JP-A-6-241017, JP-A-8-28246, JP-A-7-54643, JP-A-8-28248, etc.
However, even in the examples proposed in the aforementioned patent publications, the effect of reducing stress on segment surface is insufficient, and the problem of crack development cannot be solved completely. Also, there is a problem in that a shift in axial direction occurs between the segments during the use. Although a method in which a holding member is used to prevent the shift in the axial direction has been proposed in JP-A-6-241017, there is a problem of deformation and deterioration of the holding member occurring when the member is subject to high temperatures of exhaust gas.
As other measures for reducing thermal stress, there has been proposed a method in which a portion liable to have a relatively low temperature is heated electrically by providing an electric heater between the segments to make the temperature distribution in honeycomb structure uniform. However, this method has a problem of the occurrence of a new thermal stress because a local temperature gradient rather increases in the vicinity of the electric heater.
Also, there are a problem in that the ratio of the joint layer between the segments to the cross section is too high, so that the pressure loss of fluid is excessive, which deteriorates the engine performance, and a problem in that the heat capacity is too high, so that the rise in temperature takes much time in the regenerating treatment in which carbon particulates are burned to be removed, which prolongs the time necessary for regenerating treatment.
The present invention has been made to solve the above problems, and accordingly an object thereof is to provide a honeycomb structure in which a less thermal stress occurs during the use; durability such that no crack develops is ensured; a difference in temperature between the central portion and the outer peripheral portion is less liable to be produced; the pressure loss of fluid is low; and the time and energy necessary for the rise in temperature at the time of regenerating treatment are less.